The present invention relates generally to mechanical transmission devices in which multiple gear ratios and output shaft direction of rotation are selectively obtainable by fluid pressure actuated clutches.
While the invention is particularly adaptable to propulsion drive systems of heavy duty self-propelled vehicles such as crawler tractors, unique features herein disclosed are readily adaptable to other machines requiring variable ratio drive. A relatively few number of gears and shafts, compared to conventional transmissions, are housed in a compact space-saving housing in which the oil supply for the system is separated from the rotating components. Such an arrangement in the present invention results in more effective use of materials and greater power transmission efficiency. More particularly, this is accomplished in the present invention by placing one of the speed ratio clutches and associated gears in a cantilevered position on ends of their respective shafts and by forming a separate oil compartment in the housing so that oil splash is eliminated. The innovative arrangement of elements as well as other features including a novel arrangement of positioning the control valve on the housing in close proximity to the clutches, all tend to reduce cost, use less material and conserve energy.
Transmission housings are known that have provision for maintaining an oil supply in a compartment separate from a rotating components compartment. An example of prior art is as disclosed in U.S. Pat. No. 2,743,627 granted to H. W. Christenson May 1, 1956. However, limitations in the prior art do not permit the combination of housing structure, including a recessed portion for attaching the control valve in close proximity to work elements. Dimensional advantages are apparent in the preferred embodiment of the present invention as well as other advantages that will become apparent in the hereinafter disclosed invention.
Conventionally, multi-speed power-shift transmissions, which are frequently referred to as of a countershaft type, include a pair of friction clutches and associated gears operatively assembled on a speed clutch shaft. The speed clutch shaft is supported adjacent to its ends by bearings carried in end walls of a transmission housing. Power input to the speed clutch shaft, in transmissions having an equal number of forward and reverse speed ratios, is provided by forward and reverse clutches assembled on an input shaft that is also supported by bearings in the housing end walls. A gear on the forward clutch adjacent to one housing end wall drives a gear on the speed clutch shaft and a gear on the reverse clutch adjacent to the other housing end wall drives through a reverse idler gear to another gear on the speed clutch shaft. The reverse idler gear is carried on its own countershaft. The speed clutch shaft can therefore be selectively driven in either a forward or reverse direction by alternately engaging the forward and reverse clutches. The pair of speed ratio clutches each has a drive gear that meshes, in ratio-determining relationship, with a respective driven gear on a power output shaft. Since the pitch diameters of the speed ratio gears are chosen different for the two speed clutches, two output shaft speeds are selectively available. The aforedescribed prior art is substantially adapted in association with the present invention.
Heretofore, if more than two speed ratios are required, such as three speeds in each direction, it has been customary to provide another speed clutch shaft along with additional bearings, gears and the necessary fluid pressure transfer means. The additional number of components such as gears, shafts and bearings as well as the increased complexity of the housing in providing additional bearing bores and pressure fluid manifolds and passages, are substantially reduced in the present invention.